The saturated fluorocarbons and chlorofluorocarbons having from two to six carbon atoms are known to have superior chemical and thermal stability. Since they are relatively non-toxic and inert they have commercial utility as dielectric, hydraulic, etc. fluids. Additionally, the lower molecular weight compounds are used as propellants, refrigerants and the like. For example, trichlorofluoromethane is a heavily used blowing agent for urethane foams. The higher molecular weight compound 1,1,2-trichloro-1,2,2-trifluoroethane is a used as a solvent for cleaning circuit boards. Unfortunately, these compounds and many of the other highly chlorinated lower aliphatic hydrocarbons are known to deplete the ozone layer once they are released into the atmosphere. The fluorinated compound, 1,1-dichloro-1-fluoroethane is considered to be a viable replacement for these and similar compounds.
Among the routes to the production of 1,1-dichloro-1-fluoroethane (referred to in the art as HCFC 141b), the reaction of vinylidene chloride or 1,1,1-trichloroethane with anhydrous hydrogen fluoride have enjoyed commercial success. While yields of the desired product are economically acceptable, contamination of this material with undesirable by-products can not be avoided. For example, typically residual starting material is present in the vinylidene chloride as well as a variety of reaction by-products which include other olefins. Because of the presence of these materials, it is difficult to separate HCFC 141b from the undesirable components in the reaction mix by conventional purification processes, i.e., distillation. In the trichloroethane reaction, vinylidene chloride is a by-product. In any case, several unsaturated by-products result from these reactions which must be separated from 1,1-dichloro-1-fluoroethane before it can be used in the manner intended.
In Organic Fluorine Chemistry by Sheppard et al, W. A.Benjamin Inc. N.Y., N.Y., 1969, p 452 inhalation toxicity data are given for polyfluorochlorocarbons from tests on rats or mice. The data show that the saturated fluorochlorocarbons are inert materials. Unsaturated analogs are, however, toxic.
Numerous methods have been published on methods to reduce the amount of unsaturated compounds in saturated hydrofluorochlorocarbons.
U.S. Pat. No. 2,999,885 discloses contacting a contaminated two to six carbon saturated fluorocarbon with an aqueous solution of potassium permanganate containing an alkali metal hydroxide will result in a purified saturated fluorocarbon.
U.S. Pat. No. 5,105,035 discloses a process for removing vinylidene chloride and other unsaturated impurities from HCFC-141b by reaction with hydrogen over a catalyst such as palladium on alumina.
European Patent 39311839 (1989) discloses purification of saturated fluorohalocarbons containing unsaturated impurities by the use of metal oxides to oxidize unsaturated impurities to carbon dioxide.
U.S. Pat. No. 3,004,075 discloses the preparation of a purified saturated two to six carbon fluorochlorocarbon by contacting the impure material with a mixture of pyridine and pyrrolidine or piperidine.
U.S. Pat. No. 3,696,156 teaches that a two to six carbon saturated fluoroperhalocarbon containing olefinic impurities can be purified by contacting the olefinic-contaminated fluoroperhalocarbon in the vapor phase with alumina impregnated with a basic alkali metal or alkaline earth metal hydroxide or oxide at 180 to 250.degree. C.
U.S. Pat. No. 4,849,558 discloses that chlorofluorocarbon solvents contaminated with sulfur dioxide can be purified by contact with alumina or zeolite.
U.S. Pat. No. 4,950,816 discloses that 1,1-dichloro-1-fluoroethane containing olefinic impurities can be purified by passing the impure 1,1-dichloro-1-fluoroethane through activated carbon.
British Patent 627,773 (1949) discloses the purification of 1,1-dichloro-1-fluoroethane by chlorinating the contaminating vinylidene chloride and distilling the desired product overhead. The chlorination procedure is not described. However, vinylidene chloride is known to be stable to chlorine in the dark, e.g., see J.Chem. Soc. Faraday Trans.70 1419 (1974)), and 1,1-dichloro-1-fluoro-ethane is well known to be unstable to the Lewis acid catalysts such as FeCl.sub.3 sometimes used to catalyze chlorine additions. Accordingly, it is reasonable to assume that the chlorination was accomplished by exposing the mixture to light. Incandescent or fluorescent lamps and sunlight have sufficient output below 500 nm to initiate free radical chain reactions of chlorine.